More than likely there's something causing a fatal error in the setup program, and your machine is set to automatically reboot when that happens (it's the default in both 2kPro and XP.) You can disable this by right-clicking on My Computer, select Properties, click Advanced tab, click Startup and Recovery, and then clear out the check box for "Automatically Restart". This will probably result in a blue screen of death error message, but at least you can start diagnosing it.
Please take no offense, but would this be a "downloaded" version of Office? If so no need to respond, but you may have a data flaw in one of the setup files that's causing a major error to take place. Other possible causes would be a media problem (scratch on CD or something else). You might try copying the entire contents of the CD to your hard drive and installing from there, but you'll likely get the same error if the media is damaged.
Good luck, and let us know.